The present invention relates to a system for driving a hybrid vehicle using both of a motor and a motor/generator as the drive sources, and a method of driving the hybrid vehicle, and an electric power supply system for the hybrid vehicle.
As disclosed in Japanese Patent Application Laid-Open No. 9-65508, it is known a hybrid vehicle which generates electric power by driving an engine generator and runs by driving a vehicle driving motor using the generated electric power.
In a conventional hybrid vehicle, reduction of fuel consumption and cleaning of exhaust gas are performed by appropriately switching the drive sources corresponding to the running condition, that is, by using motor drive when exhaust gas becomes a problem, for example, when the hybrid vehicle is started or accelerated. In addition, it is an effective method for reducing exhaust gas to stop operation of the engine at an idling period.
However, the hybrid vehicle still has problems to be solved in order to extend the running distance by storing sufficient electric power in the battery and to keep good operating characteristics.
In a hybrid vehicle which reduces an amount of harmful exhaust gases by stopping idling operation of the engine when the vehicle is temporarily stopped for purpose of emission control, for example, at waiting for traffic light change, when the engine is restarted after once stopping operation of the engine, the engine can not be smoothly restarted to perform acceleration running if sufficient electric power is not stored in the battery. Further, if the environmental condition such as cooling water temperature of the engine is not within an appropriate range at temporarily stopping the vehicle, there are some cases where the engine can not be smoothly restarted just after that.
Further, the conventional hybrid vehicle uses a high voltage main battery, for example, a 120 V battery, because the vehicle driving motor requires large output. The hybrid vehicle also comprises, for example, a 12 V auxiliary battery as the power source for the engine, the other auxiliary machines, a lighting system, an air-conditioner and so on. Wiring of the main battery needs to have a dedicated ground in order to prevent a human body from electric shock because of the high voltage of 120 V. As a result, the wiring systems of the both electric power sources of the main battery and the auxiliary battery become complex. On the other hand, when the voltage of the power source of the main battery is simply lowered, it is worried that the outputs of the motor and the generator are decreased.
A first object of the present invention is to provide a system for driving a hybrid vehicle and a method of driving the hybrid vehicle which can store sufficient electric power in a battery and is excellent in the operating characteristic by solving the above-mentioned problems.
A second object of the present invention is to provide a system for driving a hybrid vehicle and a method of driving the hybrid vehicle which can smoothly restart the engine or perform acceleration running after stopping idling operation of the engine in a case where an amount of harmful exhaust gases is reduced at temporarily stopping of the vehicle by stopping idling operation of the engine for purpose of emission control.
A third object of the present invention is to provide a safe and simplified electric power supply system for the hybrid vehicle by solving the above-mentioned problems.
A fourth object of the present invention is to provide an electric power supply system for the hybrid vehicle which can improve not only operating characteristics of the motor and the generator but also operating characteristics of the engine such as the acceleration performance.
In order to attain the first and the second objects, the present invention is characterized by a system for driving a hybrid vehicle comprising an engine; a motor/generator coupled to the engine; a battery connected to the motor/generator through an electric power converter; and a controller for controlling the engine and the motor/generator corresponding to driving condition of the vehicle, wherein the controller has a plurality of operating modes for controlling the engine and the motor/generator corresponding to an accelerator opening degree for operating the engine and a charge ratio of the battery, and the controller selects an engine running electric generating mode that the engine is operated as a driving source of the vehicle and the motor/generator and electric power generated by the motor/generator is recovered to the battery when the charge ratio is low; an acceleration mode that the engine and the motor/generator are operated as the driving source of the vehicle when the charge ratio of the battery is high, and the accelerator opening degree or a rate of change of the accelerator opening degree is large; and an engine running mode that only the engine is operated as the driving source of the vehicle when the charge ratio of the battery is high and the accelerator opening degree is small.
Another feature of the present invention is that the controller stops the engine to operate as an engine stop mode when a key-switch is on, an accelerator is off and a speed of the vehicle is slower than a preset value, and the charge ratio is higher than a preset value.
A further feature of the present invention is that the controller selects the engine stop mode when in addition to the stop condition described above, an engine cooling water temperature is higher than a preset value TS and an inclining angle of the vehicle in a stopping state is smaller than a preset value xcex8.
The present invention is characterized by a method of driving a hybrid vehicle comprising an engine; a motor/generator coupled to the engine; a battery connected to the motor/generator through an electric power converter; and a controller for controlling the engine and the motor/generator corresponding to driving condition of the vehicle, wherein an engine running electric generating mode is selected when the charge ratio is low, the engine running electric generating mode being that the engine is operated as a driving source of the vehicle and the motor/generator and electric power generated by the motor/generator is recovered to the battery; an acceleration mode is selected when the charge ratio of the battery is high, and the accelerator opening degree or a rate of change of the accelerator opening degree is large, the acceleration mode being that the engine and the motor/generator are operated as the driving source of the vehicle; and an engine running mode is selected when the charge ratio of the battery is high and the accelerator opening degree is small, the engine running mode being that only the engine is operated as the driving source of the vehicle.
According to the present invention, the operating characteristics of the hybrid vehicle such as reduction of fuel consumption, acceleration performance can be improved. Particularly, since idling operation of the engine is stopped under the preset condition when the accelerator is off even if the key-switch is on, it is possible to easily reduce an amount of harmful exhaust gases at temporarily stopping of the vehicle for purpose of emission control and to easily perform the driving operation for temporary stopping and then to restart the engine or perform smooth acceleration running.
In order to attain the third and the fourth objects, the present invention is characterized by an electric power supply system for a hybrid vehicle comprising an engine; a motor/generator coupled to the engine; a battery connected to the motor/generator through an electric power converter, the battery being composed of a main battery and an auxiliary battery, wherein the auxiliary battery is connected to the main battery through a switching element and controlled to a voltage lower than a voltage of the main battery, a ground line being commonly used by the main battery and the auxiliary battery, the auxiliary battery being charged from the main battery through the switching element depending on a charge ratio of the main battery when the main battery stores enough electric power.
Another feature of the present invention is that voltage of the main battery is not higher than 60 V, and voltage of the auxiliary battery is 12 V or 24 V.
A further feature of the present invention is that the main battery is used for an electric power source of electromagnetic coils for driving an injector and an intake and an exhaust valves of the engine.
According to the present invention, since the voltage of the main battery is set low, for example, below 60 V, and the ground line being commonly used by the main battery and the auxiliary battery, all the power source lines wired inside the vehicle are positive voltage lines and accordingly the electric power units of the hybrid vehicle can be simplified.
Further, since the high voltage main battery is used for the electric power source of electromagnetic coils for driving the injector and the intake and an exhaust valves of the engine, it is possible to provide a hybrid vehicle which can improve operating characteristics of the engine such as the acceleration performance by improving the operating response of these constituent parts of the engine.